Brad, if you hook up a transfer switch, one will be 'hot', and one feed 'not' it will be automatic. The hot one will energize the contactor coil, pull in the contacts, the other contactor will be open, with no power to the coil. That is what I have wired, I just have the inverter-generator feed to one contactor and coil. That way, you would have no backfeed to the unused power supply.
Here's some reading and refrence:
http://www.pplmotorhomes.com/parts/r...fer-switch.htm
http://www.iotaengineering.com/pplib/50rint.pdf
http://www.iotaengineering.com/its50r.htm